Aquatic net cages or pens of various shapes and sizes have been used for many years to contain fish for the purposes of research, breeding and raising fish for food. Cages designed for the breeding and/or raising of fish for consumption either float or rest at the bottom of an outdoor body of water. Generally, such cages have an access opening in the top of the cage and are often designed to retain man-made fish food within the cage by providing an overlay of netting on the cage bottom with a mesh size that is substantially smaller than the other netting that covers the cage. Such cages may also include fish grading screens of either netting or parallel bars to separate the smaller fish prior to harvesting the larger fish.
Aquatic net cages for research purposes are also known. For example, some cages are designed to study the effect of pollutants on fish growth. However, such cages are often designed to isolate the different species being studied from each other and/or predators. Thus, such cages have a very specialized research purpose and a relatively complicated construction. In other studies, round cages suspended in a body of water may be used to study the predatory behavior of fish populations.
It is also known to use cages that rest at the bottom of a body of water to study in situ fish growth. Fish growth is affected by environmental conditions, such as the availability of food, dissolved oxygen concentrations, water temperature, pollutants, etc. Therefore, in contrast to cages in which fish are raised for consumption, in fish growth studies, preferably, all of the food should come from the local environment; and no man-made food should be provided. Cages to study fish growth are often bottomless, so that the plant and animal life is readily available as food for fish being studied. However, a bottomless cage has several disadvantages. First, access to the cage is through a relatively small opening or door generally in the top of the cage, and thus, removal of fish from the cage must be done with a dip net or suction gun. In turbid water in which the visibility is limited, the removal of fish from a bottomless cage with a dip net or other device is very difficult and time consuming. In very turbid water with close to zero visibility, such a task is almost impossible. Further, deploying and retrieving fish in a bottomless fish cage in turbid water from a boat is also very difficult if not impossible. Therefore, fish growth studies using bottomless cages must be limited to less turbid or shallower waters. Further, in view of the difficulties in handling fish in a bottomless cage, such cages are often made smaller, thereby severely limiting available food supply and thus, the number of fish that can be studied in each cage.
Therefore, there is a need to provide an improved fish cage for in situ fish growth studies that does not have the disadvantages of known cages.